The present invention concerns a method for controlling the grilling, or toasting, of a food product in a toaster, and more particularly the use of one or several photosensitive sensors for carrying out this control.
It is known, in bread toasting appliances, to provide a time delay that is adjustable by the user, in order to fix the cooking time for the bread. This simple method does not always give satisfactory results, notably because of lack of initial knowledge of the time necessary to obtain a given toasting or color for the bread.
Other systems propose a determination of the color of the bread during the course of toasting with the aid of a specific sensor measuring the reflectivity, produced by the bread, of a light signal.
The document WO89/01279 describes such a sensor using an electronic control circuit for an electric device for cooking food products having a maximalizing circuit intended to determine, by a first signal V1, the maximum level of light reflected by the food product, then to measure the light reflected by the food product leading to a second signal V2, the maximalizing circuit having an amplifier supplying a signal V3 proportional to the difference between the V2 and V1, a comparator permitting a comparison of V3 with a preset signal VB, which is proportional to a desired cooking level. The comparator emits a signal at the end of cooking to deactivate the cooking when the preset signal and the third signal are substantially equal. The signal V2 is constructed around a resistance whose value depends on the quantity of incident light. Such resistances are commonly called LDR.
Such a devices is rather complex and costly with regard to elements since it comprises several electrical signals to compare, amplifiers, comparators and necessitates the establishment of a comparison voltage value VB.
Moreover, from the standpoint of security, a conventional time delay requires a safety device detecting the start of burning of the bread and any presence of flames in the toaster.
In addition, when the power of the heating elements is substantial, it is necessary that the device have a significant response, a response that conventional time delays cannot provide.
The present invention seeks to overcome these drawbacks by providing a simplified process for controlling the degree of browning of a food product disposed in a grilling appliance, by the evolution of the light coming from the food product being grilled.
The present invention is achieved with the aid of a method for controlling the grilling, or toasting, of a food product placed in a grilling appliance of the toaster or oven type, said appliance comprising, in particular, heating elements, a heating chamber, a grilling selector for adjusting the level of browning of the food product, means for stopping the supply of electricity to the heating elements when the level of toasting is achieved, said device having a light-receiving system composed of at least one photo-resistive element of the LDR type, the light reflected by the food product being grilled or toasted being brought up to the surface of said element(s), characterized in that it consists in measuring the evolution in time of a signal G representative of the light reflectivity of the food product, and converting at least one characteristic of that evolution into at least one of the grilling or toasting states of the food product.
According to the invention, one of the grilling or toasting states is manifested by a slope of the signal G stabilizing at a determined value, or by a zero slope, or by an inversion of the slope, or by a point of inflexion in the slope of the curve, or by a difference in the curve or in the slope of the curve by a certain amount with respect to said value for shorter times.
The grilling states being correlated with a particular evolution of the signal, this curve becomes universal and a simple calibration in the factory permits establishment of the desired relationships.
Advantageously, this method consists equally in determining the ambient temperature within the appliance, and in blocking a new cooking cycle when the value of the ambient temperature exceeds a predetermined value.
This particularity is notably important for high heating power levels being able to lead to, when numerous cycles are effectuated, a temperature elevation that could be dangerous for the user.
Advantageously, the method also consists in determining the signal representative of the light reflectivity at two instants that are close together and following the application of electricity to the heating elements in order to determine, according to the evolution of this signal, the presence or not of a food product in the heating chamber.
It can be, in effect, desirable, for example in the case of a toaster, to block the operation of the appliance when no slice is placed to be toasted in the heating chamber. A rapid decrease in the light reflectivity signal permits the absence of bread to be identified.
Advantageously, the method for controlling grilling consists equally in halting the supply of electricity to the heating elements when, following the start of delivery of electricity to said heating elements, the light reflectivity signal is below a predetermined value.
This system permits avoiding, on the one hand, regrilling a food product that has already been grilled, and, on the other hand, blocking the toasting of special breads, of which the presence of grains or other ingredient gives it a dark color. It is known that this bread is difficult to toast, the automatic toasting procedure such as described previously is thus not desirable.
Advantageously, the method for controlling grilling is associated with a method for controlling grilling with a time delay where different grilling states, determined by the grilling selector, correspond to cooking times calibrated in the factory.
Thus, the device for controlling by a photo-resistive element only determines certain grilling states or is used, for safety purposes, as a fuse.
Another object of the present invention, is to provide a low cost system permitting toasting of any type of bread, stale or frozen, by controlling the toasting color assumed by the bread, and this regardless of the parameters of use or characterization of the toaster: duration of stoppage between cycles, partial or complete loading of the bread carriage, variation of the power supply voltage, power and type of heating bars.
The present invention also has for its object a device for controlling the grilling of a food product placed in a grilling appliance of the toaster or oven type, said appliance comprising notably heating elements, a grilling selector permitting adjustment of the level of browning of the food product, means for stopping the supply of electricity to the heating elements when the grilling level is attained, a microcontroller, said device having a light receiving system composed of at least one photo-resistive element of LDR type, the light reflected by the food product being grilled being brought up to the surface of said element(s), inserted in an electronic circuit permitting measurement of a voltage, characterized in that this voltage is transformed into a signal G which can be the value of the resistance of the photo-resistive element or of one of the photo-resistive elements, or a magnitude proportional to said resistance, said signal being stored at successive instants in the microcontroller, in order to determine the evolution of said signal and to stop the heating elements according to at least one predetermined evolution criterion.
This device permits freedom from numerous variables determining the grilling of the food products and notably of bread and which can vary in an undesirable manner with the level of voltage of the supply mains, or according to the heating powers used or the aging of the heating elements, for example.
According to the invention, the predetermined evolution criteria represent different grilling states of the food product.
According to a first embodiment of the invention, the signal is constituted by the value of the resistance of the photo-resistive element or of one of the photo-resistive elements, obtained by measuring the voltage at the terminals of this element in a dividing bridge arrangement, said voltage being sent to an analog input-output port of the microcontroller.
This arrangement, very simple to achieve, permits, by a simple voltage measurement, to obtain the characteristic parameter of the light sent to the sensor by the food product.
According to a second embodiment, the signal is constituted by the time for charging a capacitor through the resistance presented by the photo-resistive element or one of the photo-resistive elements, that is an analog/digital conversion system, each element being associated with a capacitor and connected to numeric inlet-outlet ports of the microcontroller.
This arrangement permits the use of a microcontroller having only numeric inputs, which reduces the cost of the component.
Advantageously, according to the first or second embodiment, the grilling control device has at least two photo-resistive elements, the signal G being successively and cyclically determined for each photo-resistive element.
By providing several photo-resistive sensors, the evolution of which is followed in parallel, and step-by-step, the determination of the overall grilling state of the food product is improved. In effect, the evolution of several sensors increases the reliability of the determination of the degree of grilling achieved.
Moreover, when the device is used in a toaster, by disposing sensors at each side of the heating chamber, it is possible to follow the evolution of each surface of the bread, and to modify the supply of electricity to the heating elements for each surface, whether the bread surfaces are initially identical or not, in order to obtain a uniform grilling on each of the surfaces of the bread, or in order to stop the heating elements in order to avoid charring of one of the surfaces of the bread.
According to this construction, stopping of the heating elements is triggered as soon as the evolution of the signal of one of the photo-resistive elements attains the predetermined evolution criteria. This solution permits avoiding all risk of charring of one part of the food product when several pieces are introduced.
According to a construction variant of these different embodiments, the laws of behavior link the evolutions of the signal of the different photo-resistive elements in order to determine the operating state of the appliance.
By using several photo-resistive elements, according to the evolution of the signal representative of the light received, different conclusions regarding the presence of the food product and regarding the nature of their surface (for example the soft part and the crust of the baguette) can be determined. According to certain predefined schemes, different actions can be envisioned.
Advantageously, a light guide connects the heating chamber of the appliance to the photo-resistive sensor situated on an electronic card spaced from the heating chamber. This device permits the electronic card to be held at a distance from the heating chamber where elevated temperatures can damage said card.
Advantageously, a filter, such as an IR filter is disposed in front of each photo-resistive element in order to contrast the response curve of the LDR sensor.
Another object of the present invention is to provide a grilling control device on a large spatial surface, in order to be free of the hazards of distribution of the food products to be grilled on the receiving device provided for this purpose.
This object is achieved with aid of a device for controlling the grilling of a food product placed in a grilling appliance of the toaster or oven type, said appliance comprising notably heating elements, a heating chamber comprising a surface for introduction of the food product, a grilling selector permitting adjustment of the level of browning of the food product, means permitting stopping of the electric supply to the heating elements when the browning level is attained, said device having a light receiving system composed of at least two photo-resistive sensors of the LDR type, characterized in that the sensors are arranged on a line parallel to the surface of introduction of the food product, facing said food product.
By such an arrangement, one increases the observation coverage of the food product that is to be grilled, while avoiding that the food products are disposed in the heating chamber without being detected by the sensor when there is only one.
According to a preferred form of construction of the invention, the grilling control device has three sensors equidistant from one another, the central sensor being substantially disposed facing the heating chamber, in its central plane.
The use of three sensors appears to be a good compromise between the coverage proposed by the assembly of these sensors, relative to the viewing angle of each sensor, and this, whether the appliance is a toaster or an oven. The equidistance and the centering of the sensors optimizes the coverage of these zones.
Advantageously, the sensors are inclined with respect to the plane of introduction of the food product by an angle between 30 and 90.
This inclination permits the coverage of the observed zones to be increased, while offering the possibilities of protection from the radiation emitted by the heating elements.
The present invention aims equally at the construction of a cooking appliance of the toaster or oven type, characterized in that it includes a process for controlling grilling of food products such as previously described.
Another object of the invention relates to a cooking appliance of the toaster or oven type, characterized in that it has a device for controlling the grilling of food products such as previously described.